Project Summary The acquisition of iron is an essential process for the establishment of virulence among virtually all pathogens. To fulfill its necessity for this nutrient, the Gram-negative bacterium Porphyromonas gingivalis (the causative agent of chronic periodontitis) makes use of two main iron uptake pathways to grow and to proliferate. Under anaerobic conditions, such as those found in subgingival biofilms, P. gingivalis utilizes the ferrous (Fe2+) iron uptake (Feo) system to import Fe2+. The Feo system is poorly understood at the molecular and mechanistic levels, but two proteins known as FeoA and FeoB are necessary for ferrous iron uptake in most pathogens. This proposal seeks to explore the role of FeoA in controlling FeoB function. Based on preliminary data and previous observations, it is hypothesized that the conserved protein FeoA functions as a novel, prokaryotic G-protein regulator that is necessary to control the GTP-utilizing, integral membrane protein FeoB. The P. gingivalis genome offers a unique opportunity to explore the role of FeoA with respect to FeoB, as the feo operon in this organism indicates that FeoA and FeoB are expressed and function as a single protein. This proposal outlines a series of biochemical, structural, enzymatic, and in vivo approaches to explore and to elucidate the potentially novel role of FeoA in controlling Fe2+ transport mediated via FeoB. The results from these studies have the promise to reveal how FeoA is utilized by the common pathogen P. gingivalis to fulfill its need for iron. A similar thethered FeoA-FeoB system is predicted to exist in other pathogens implicated in periodontal disease, such as Tannerella forsythia, Porphyromonas endodontalis, and Porphyromonas gulae. As such, it is anticipated these results will uncover a general regulatory mechanism present in many oral pathogens. More broadly, these studies will lay the groundwork for future research to understand how many pathogens use FeoA in conjunction with FeoB to establish infection. Future studies have the potential to reveal targets for the development of therapeutic interventions and novel antibiotics.